Cook the chicken by boiling it in water for about 25 minutes until fully cooked, then shred it.
Preheat the oven to 350°F and prepare a baking pan with non-stick spray.
In a medium saucepot, combine cream cheese, ranch dressing, hot sauce, black pepper, and garlic powder over medium-low heat until smooth.
Mix in the shredded chicken, green onion, and one cup each of mozzarella and cheddar cheese, then transfer to the baking pan and top with remaining cheeses.
Bake for 20-30 minutes until cheeses are melted and bubbly, then broil for 2-3 minutes for a golden finish.
Let cool slightly before serving with tortilla chips, veggies, or crackers.